Unsupported thin wall gloves are made via a dipping procedure from materials including natural rubber latex, polychloroprene, polyisoprene, carboxylated acrylonitrile butadiene, styrene butadiene copolymer, polyurethane and blends of these materials. The material is an aqueous emulsion form with natural rubber latex being concentrated and preserved prior to use and synthetic rubber materials polymerized via emulsion polymerization.
In the dipping procedure, a hand shaped former is lowered into the compound causing a thin layer of the compound to deposit on to the former. After vulcanization, the gloves are removed from the former. In addition to gloves, condoms and balloons are also formed in this manner.
The former is lowered into the compound with the fingertips entering the tank first and coming out last. The fingertip portion of the former, therefore, has a greater time in the compound known as dwell time. The greater dwell time results in a thicker layer of compound at the fingertips and thinnest at the cuff. This thickness is designed as the thinner cuffs are more prone to tearing when the gloves are donned and thicker fingertips are a hindrance when the wearer performs intricate tasks. Tests on 30 products from difference manufacturers found a thickness gradient of 0.1 mm at the palm and 0.18 mm at the fingertips.
In addition to dwell time, other factors impact the thickness of material deposited on the former. To insure uniform deposition, a coagulant, such as calcium nitrate solution with appropriate additives such as ionic and non-ionic surfactants, mold releasing agents and other conventional additives are employed in the compound. The higher concentration of coagulant the thicker the film formed on the former. In addition, a latex compound having a higher solid content results in a thicker film. To a lesser extent, the temperature of the former affects thickness as a lower temperature tends to result in a thicker glove. Regardless of these factors, the introduction of the former fingertip first into the compound always results in the finger tip having a greater dwell time than the cuff and is a factor weighing in favor fingertips having a greater thickness than the cuffs.
Attempts to address this problem are found in previous patents. U.S. Pat. No. 3,397,265 describes a multiple dipping process including dipping the full length of a former into a concentrated coagulant, dipping the former having the coagulant into water below the wrist to remove the coagulant from the palm and fingers, dipping the former into diluted coagulant to have a varying concentration of coagulant along the former and then dipping the full length of the former into a latex compound.
Practical difficulties with this method is the contamination of the water tank with coagulant that is removed from the former. The concentration of the coagulant within the water tank increases with each successive former introduced into the tank. Also, a large amount of coagulant is wasted by removal by the water.
U.S. Pat. Nos. 3,859,410 and 3,843,196, both to Sidley, disclose a multiple dipping process including dipping a former into a concentrated coagulant with cuff portion first followed by dipping the former into a diluted coagulant fingertips first to a level below the wrist to achieve a varying concentration of coagulant followed by dipping the former, fingertips first, into a latex compound tank. This requires a specially designed machine in order to invert the former. Also, the holder of the former is immersed into the coagulant tank leading to an inevitable contamination.
It is an object of the invention to provide a dwell having a more uniform thickness between cuff and fingertip.
It is another object of the invention to provide a glove having additional coagulant at the cuff to result in a thicker cuff.
It is another object of the invention to provide a method for making the glove having a varying amount of coagulant along the former.
It is another object of the invention to provide a method for having a thicker cuff made by a method without contamination of the separate tanks used in the method.
These and other objects of the invention will become apparent to one of ordinary skill in the art after reading the disclosure of the invention.